Burnham replacement boiler EDR/Pick Up Question

Local1Plumber · May 23

Hey all, this past winter my residential boiler has finally had it. A crack in one of the sections has me heating the atmosphere lol. That said, contrary to what my knees want I will be replacing it this summer and am trying to appropriately size up my replacement. I own "The Lost Art of Steam Heat" for a while now and have been going over all the calculations. Essentially I have about 353 EDR (radiators/blind riser) no pick up factor added in. If I add a 1.33 pick up its roughly 470 EDR. If I multiply 470 X 240 (btu) I will need around 113,000 btu boiler. In regards to a Burnham I'm looking at a "STMX150". Am I missing anything? Again this is for my home so I'm not trying to get "free" advice for help pricing a job. An extra set of eyes is appreciated. Thanks for stopping in.

STMX150NRHPA.pdf

ChrisJ · May 23

That will work but if it was mine id go with the STMX125.

But personally id recommend a WM EG40 or a Peerless.

Steamhead · May 23

@Local1Plumber , the boiler's square feet rating has the pickup factor built in. If you're going to use a SteamMax the 150 is the right choice. But make sure your steam pipes are insulated and your main vents are properly sized.

Is this a one-pipe system?

Jamie Hall · May 23

You could just compare your EDR to the EDR rating of the boiler — no conversions needed, the pick up factor is already worked into the boiler rating…

mattmia2 · May 23

is it 1 pipe or 2 pipe? you can undersize a fair bit with 2 pipe without ill effect. even with 1 pipe slightly under is better than a lot over. unless you have a whole lot of main and riser piping the actual pickup of the system is probably more like 10%.

Alan (California Radiant) Forbes · May 23

353 EDR (output without a pickup factor) x 240 BTU/EDR = 84,720 BTU's.

Why couldn't he go with a Burnham STMX100 which has an output of 82,000 BTU's?

mattmia2 · May 23

https://forum.heatinghelp.com/discussion/comment/1897215#Comment_1897215

the pickup factor covers things like losses from the piping and an output greater than the steady state to heat the system at the start of a cycle. you do need some pickup factor, just usually far less than 30%. the 100 is probably too small unless it is 2 pipe but the 125 is probably perfect.

EBEBRATT-Ed · May 23

@Local1Plumber

You nailed it

Alan (California Radiant) Forbes · May 23

So, what would be the best choice? Burnham, WM or Peerless? Let’s say his installer would be happy with any of them and there are local suppliers for all brands.

Steamhead · May 23

https://forum.heatinghelp.com/discussion/comment/1897221#Comment_1897221

I'd go with Peerless.

STEAM DOCTOR · May 24

Peerless or Williamson. No need to waste money on a WM jacket.

Local1Plumber · May 28

Hey all thanks for lending your eyes, time and knowledge. Steamhead and Mattmal2 — my system is a one pipe parallel flow (mostly), dry return system. I installed two, #2 Gorton and of main air vents a few years back (set back from the dry return drop, manifold style and up on a nipple with a screen, etc.) and the pipes are insulated. I also added some vents at the top of the risers and set the radiators back with a straight radiator vale and because I nerd out on all the steam ideology I also threw on Danfoss valves for the radiators.

—ChrisJ, you think the STMX125 will suffice? It'll be less expensive which is good but I tend to err on the side of slightly larger but I'm open to it if it'll work appropriately.

ethicalpaul · May 28

For steam, learn to err on the slightly smaller. But it won't be an err, it will be the correct thing to do.

mattmia2 · May 28

the stmx125 gives you over 10% pickup factor, especially with the TRVs i think that will be fine.

ChrisJ · May 28

https://forum.heatinghelp.com/discussion/comment/1897504#Comment_1897504

There's no reason to err on larger in this case.

All it'll get you is noisier vents and the inability to do large recoveries.

I started with an EG-45, which is the same as the stmx150. 150,000 input and I have 392sqft of radiation.

After a few years I dropped it down to an EG40, which is the same as the stmx125. It heats the same, but a bit slower so it's easier for the thermostat to control and vents stay quiet. I can also do an 8-10 degree recovery if I want.

EBEBRATT-Ed · May 29

Even with the 125 boiler you will have a PU factor of 21%.

this means you have 21% more capacity than the radiators will condense. Although you are supposed to size a boiler based on the radiator EDR you can use a little common-sense thinking.

You could always do a heat loss calculation.

If the HL calculation is considerably less than the radiation output (and it probably is) then consider the smaller boiler.

Local1Plumber · May 29

Hey friends, all solid advice and EBERATT-Ed I agree some common sense thinking is appropriate here. EthicalPaul and mattmla— fair point(s) on the err not being an err and leaning smaller with pickup, insulation and TRX valves it'll slow it all down and heat more evenly, thanks. ChrisJ — your "real world" experience example sounds just right, thanks. I'll get going on it and keep everyone updated with some pictures. Thanks!

EdTheHeaterMan · May 29

You are on the correct path here @Local1Plumber. I know it is sometimes scary trusting your knowledge and calculations for a job that ends up with a much smaller appliance input that the old system. I remember the first time I did an actual heat loss for a water boiler, and decided to propose the smallest size boiler out of three other competitors. At the time, I was not charging enough since I was new to being self employed and didn't know my reals costs yet. So my price was also very attractive. But the customer asked "What if the heater isn't big enough to heat my house?" I replies with confidence that I would increase the size at no additional cost for labor and only $150.00 extra for the larger boiler cost.

When I got the job, I was so scared that I double checked the heat loss calculation numbers a second and third time before I ordered the boiler. After removing a boiler the size of a Volkswagon Beetle and opening the crate with a bopiler the size of a suit case, the customer asked "Are you sure…". I said "YES" with confidence I didn't really have. Boy was I glad it heated everything properly. Even on a extremely cold day in January. I called the customer to se if the radiators were keeping up with the thermostat. and they were. Now I have all the confidence in the world that just about every heater ever installed by anyone in the 1950s and earlier IS TOO BIG !!!

So you have the proper size boiler with the 125. You did your homework correctly and by the way, you don't need to do all that math to select the boiler size. You count the EDR and use the Sq Ft steam Net rating. The math is already done by the manufacturer for you.

KC_Jones · May 29

https://forum.heatinghelp.com/discussion/comment/1897504#Comment_1897504

As someone who is currently running a 1 pipe system with a boiler that is firing under the EDR of the system, I'd go with the 125 and not even think about it. Smaller is glorious. That said, let's run the numbers for your system, keeping in mind the 125 is still "oversized".

353 system EDR=84,720 BTU

SteamMax 125 gross output 103,000 BTU

18,280 "pickup" or 76 EDR

Gives a pickup percentage of 21.5%, it's not 33%, but it would be enough to support 122' of uninsulated 2" main piping, so I think you will be good.

Having just come through a very cold winter with my "too small" boiler I can tell you it was amazing. We had many days in a row below design temps. I had run times lasting for hours, kept the rads nice and toasty that whole time. It was super comfortable, but most of all it was dead silent. Not a peep of noise from anything ever. That's what 1/2" of pressure gets you, glory. This is how steam was meant to run IMHO.

Burnham replacement boiler EDR/Pick Up Question

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